1. Field of the Invention
This invention relates to a method for immunoassay, particularly to a method for immunoassay in which an antigenic substance which is apparently electrically neutral or has no or slight electric charge is electrified to be enabled to migrate by electrophoresis, or in which an antigenic substance which has an electric charge is more electrified to be improved in migration property, whereby the substance is advantageously quantitated.
2. Related Art Statement
A typical example of immunoassay which have been made practicable heretofore is radioimmunoassay. However, radioimmunoassay requires troublesome operations. Therefore, a highly sensitive immunoassay utilizing electrophoresis was developed. A method related to this immunoassay is disclosed, for example, in U.S. Pat. No. 4,628,035. In this immunoassay using electrophoresis, a reaction carrier is provided between an anode and a cathode in electrophoretic apparatus, and an antibody reactive specifically with a substance to be determined has been previously attached to the reaction carrier. The substance to be determined is allowed to arrive at the reaction carrier by electrophoretic migration and subjected to antigen-antibody reaction with the antibody reactive specifically with the substance to be determined in the carrier. According to this method, upon quantitating a substance to be determined in a sample, contaminating materials in the sample which cause measurement errors are merely passed through the reaction carrier by electrophoresis and prevented from being held therein, and hence they do not affect the antigen-antibody reaction in the reaction carrier. Therefore, according to this method, the good precision of measurement can be achieved, and even trace constituents of blood can be determined with high sensitivity because the substance to be determined is concentrated in the reaction carrier by electrophoresis.
However, for analyzing a substance to be determined by the above method the arrival of the substance to be determined at the reaction carrier by electrophoretic migration is an essential. When the substance to be determined is one which has an electric charge such as a protein component, the immunoassay utilizing electrophoresis can be effectively practised. However, electrophoresis is not applicable to a substance to be determined which has no electric charge. Therefore, the above method is disadvantageous, for examples, in that quantitation of a substance which is apparently electrically neutral or has no or slight electric charge is not taken into consideration, so that quantitation of a hapten such a steroidal hormone is difficult. Furthermore, the above method is disadvantageous in that where a substance to be determined which has originally an electric charge exists in a sample at very low concentration, the substance becomes not to have a high migration property and therefore the substance can not be determined with high sensitivity.